Systems And Methods For Protecting Subsea Pipeline From Excessive Stress Or Fatigue Loading.

ABSTRACT

Disclosed are systems and methods for protecting subsea pipeline from damage caused by excessive stress or fatigue loading caused by geo-hazards, and environmental and operating loads. The systems and methods utilize lifting buoyancy modules capable of being attached to a section of subsea pipeline to lift the subsea pipeline off the seabed to a predetermined height over a predetermined length upon being activated by a planned or unplanned triggering event.

This application is a divisional application claiming priority toco-pending application U.S. patent application Ser. No. 13/836,363,filed Mar. 15, 2013.

FIELD

The present disclosure relates to systems and methods for protectingsubsea pipeline and risers from damage caused by excessive stress orfatigue loading, and more particularly systems and methods utilizingbuoyancy modules capable of being attached to a subsea pipeline or riserand lifting the subsea pipeline or riser off the seabed.

BACKGROUND

As subsea hydrocarbon production systems have evolved over time, certainchallenges have become more problematic. One challenge is that subseapipeline systems now traverse greater distances often at great depths.Another challenge is that certain subsea production fields necessitateinstalling subsea pipeline across difficult geographical formationsalong the seabed, including canyons, scarps and rough terrain, or inareas of high risk for geo-hazards such as mudflows, earthquakes, soilliquefaction and soil instability. Locating a pipeline in relation tosuch areas is of concern because it may be damaged by an impactgenerated by a geo-hazard, such as a mudslide or mudflow across thepipeline. A pipeline can also be damaged by fatigue due to vortexinduced vibration or cyclic pipe movements due to slugging of the fluidflowing therein. Dynamic structures such as marine risers connected toplatforms are susceptible to fatigue damage, as are pipeline scarpcrossings with long unsupported spans. Very often these dynamicstructures tend to have certain locations in which fatigue loading ismore concentrated, such as sections near the touchdown point regions insteel catenary risers.

Conventionally, pipeline systems are designed to resist or withstand theforces associated with such geo-hazards. Detailed geo-hazards surveysand analyses are conducted to estimate the likelihood and severity of ageo-hazard event and associated loads on the pipeline. Current designprocesses, which involve multiple complex uncertainties, aim to assessthe behavior of the pipeline when subject to extreme loading conditionsand pursue a pipeline design that will sustain the impact forces andlimit the risk of catastrophic failure. Current design mitigationsinclude pipeline routing selection, engineered terrain excavation,horizontal directional drilling, stringent pipeline manufacturingstandards, installation procedures and qualification testing, and theuse of special materials, flexible elements, anchoring, and the like.These mitigations are very expensive and may have limited effectivenessto address the risks. Once there is damage to a producing pipelineleading to failure such as a rupture, current methods for containment ofspills and repair solutions are limited. Pipelines, risers and scarpcrossings are also often subject to operating and environmental loading,which can lead to cyclic stress in the pipe structure. This requiresdesigning pipeline with high quality standards of fabrication to endurefatigue loads, such as tight tolerances, stringent welding standards andweld flaw acceptance criteria, limitations during installation andoperation, qualification testing, etc.

It would be desirable to have an economical, reliable means forprotecting subsea pipeline and riser systems from excessive loadsassociated with geo-hazards, environmental loading and operating loadingand a response intervention method which could prevent significantproduction disruption. In addition it would be desirable to have a meansto alleviate fatigue damage in critical regions of the pipeline andriser systems in a planned or contingency situation.

SUMMARY

In one aspect, a system is provided for protecting subsea pipeline orrisers from excessive stress and/or fatigue loading associated withgeo-hazards, environmental loading and operating loading. The systemincludes a plurality of lifting buoyancy modules capable of beingattached to a subsea pipeline or riser wherein each of the plurality oflifting buoyancy modules has an activation mechanism associated therewith and wherein the plurality of lifting buoyancy modules hassufficient buoyancy when at least a portion of the plurality of liftingbuoyancy modules is activated to lift the subsea pipeline or riser offthe seabed to a predetermined height over a predetermined length.

In another aspect, a method is provided for protecting subsea pipelineor risers from excessive stress and/or fatigue loading associated withgeo-hazards, environmental loading and operating loading, in which theplurality of lifting buoyancy modules is attached to a subsea pipelineor riser.

DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims and accompanying drawings where:

FIGS. 1A and 1B are views of a pipeline system fitted with liftingbuoyancy modules according to one exemplary embodiment.

FIGS. 2A-2E are views of a pipeline system fitted with inflatablelifting buoyancy modules according to one exemplary embodiment.

FIGS. 3A and 3B are views of a pipeline system fitted with liftingbuoyancy modules according to another exemplary embodiment.

FIGS. 4A-4D are views of a pipeline system fitted with lifting buoyancymodules according to another exemplary embodiment.

FIGS. 5A and 5B are views of a riser system fitted with lifting buoyancymodules according to another exemplary embodiment.

FIG. 6 is a flowchart describing methods according to other exemplaryembodiments.

DETAILED DESCRIPTION

The systems and methods disclosed herein are particularly useful forprotecting subsea pipeline and risers from excessive stresses or fatigueloading associated with a variety of geo-hazards, environmental loadingand operating loading. Throughout the present disclosure, it should beunderstood that systems and methods applicable to pipeline are alsoapplicable to risers, pipelines crossing irregular features such asscarps, spans, or unstable areas subjected to potential geo-hazards. Thegeo-hazards can include sudden, one-time events or gradual long-termprocesses that can result in damage to the subsea pipeline over time.Examples of sudden events include mudflows or mudslides, earthquakes andearthquake induced soil liquefaction and sudden instability in freespans caused by sudden shifting in the seabed. Examples of gradualprocesses that can result in damage to the subsea pipeline includeseabed settling over time and other known gradual geo-hazards. Thesystems and methods disclosed herein can be employed to respond or reactto a triggering event. The triggering event can be a geo-hazard, apredictive event leading to a geo-hazard (such as increase in currentmagnitude) or a change in design conditions that requires somemitigation. The deployment of the mitigation can be sudden, almostimmediately after the triggering event, or the deployment can be plannedin such a way that the project team has a period of time to implementthe mitigation after the triggering event or after a warning sign hasbeen identified and communicated. Alternatively, the systems and methodsdisclosed herein can be employed on a proactive, planned basis to avoidstresses or fatigue loading associated with geo-hazards, environmentalloading and operating loading. The systems and methods disclosed hereincan be employed either temporarily or permanently.

One embodiment of a system 10 implemented on a subsea pipeline locatedon a seabed 7 is illustrated in FIGS. 1A and 1B. FIGS. 1A and 1B furtherinclude a scarp 11 in the seabed 7 over which the pipeline 1 crosses. Aplurality of buoyancy modules 12A having engineered liftingcapabilities, also referred to herein as “lifting buoyancy modules,” isprovided which are capable of being attached to a subsea pipeline 1. Bya plurality is meant two or more. The lifting buoyancy modules 12A arespaced at an engineered frequency. As illustrated in FIG. 1A, thelifting buoyancy modules 12A are normally in a non-activated state inwhich they either do not apply buoyancy force to the pipeline or applyinsufficient buoyancy force to lift the pipeline off the seabed 7. Thisis also referred to herein as the “normal, non-activated state” of thelifting buoyancy modules. The lifting buoyancy modules can be activatedby one of a number of activation mechanisms to be described herein. Insome embodiments, the activation mechanisms are in communication with atleast one sensor 18. As shown, the sensor 18 can be located on thepipeline 1 (or riser) or on the seabed 7. In one embodiment, the sensorcan be located in the path of an anticipated geo-hazard.

When in the activated state, the lifting buoyancy modules havesufficient buoyancy force acting on the pipeline (or riser) to lift thesubsea pipeline off the seabed. The activation of the lifting buoyancymodules causes the buoyancy force to exceed the pipeline submergedpipeline weight. The lifting buoyancy modules lift the pipeline off theseabed to a predetermined height H over a length of the pipeline. Thepredetermined height and length are advantageously sufficient to avoidthe impact of a geo-hazard, to alleviate the fatigue damage or to reducestress levels. Alternatively, the height can be variable as determinedbased on a sensor and processor system that detects leading geo-hazardevents and calculates the required height to avoid geo-hazards, e.g.,mudflows. The variable height lifting buoyancy module can be achieved bycontrolling the final volume of the buoyancy or by controlled activationof the sequence and number of deployed buoyancies.

Unlike existing pipeline systems in which the pipeline remains in placeon the seabed and is subject to significant loads generated by ageo-hazard, e.g., a mudflow, the systems and methods disclosed hereinallow the pipeline to escape such loads by lifting the pipeline abovethe mudflow height to protect the pipeline from displacing laterally sothat the pipeline retains its integrity. Additionally, unlike existingdynamic pipeline, riser and scarp crossing structures in which thesystem is subject to continuous loading, the systems and methodsdisclosed herein alleviate the stresses, reduce the stress cycles and/ordistribute the concentrated stresses imposed on the structures forimproved structural protection, endurance and integrity.

In some embodiments, the system can be designed so that the pipeline islifted in a controlled or progressive manner This can be advantageous toavoid inadvertent damage to the pipeline caused by large buoyancy forcesuddenly applied to the pipeline. This can be accomplished by providingdifferent levels of buoyancy force on the pipeline to lift the pipelineoff the seabed at different rates. The system can be designed so thatone or more lifting buoyancy modules of a given system are activatedseparately, simultaneously or in a timed sequence in accordance withsensor inputs or in accordance with a preprogrammed, planned sequence.

The activation mechanism for activating the lifting buoyancy modules canbe activated or triggered by a signal sent to the activation mechanismfrom one or more sensors 18. In one embodiment, a sensor 18 is includedin the system in communication with the activation mechanism of each ofthe plurality of lifting buoyancy modules for sensing the onset of atriggering event. The triggering event can be indicated by apredetermined ocean current magnitude ahead of sliding mudflows,turbidity caused by an approaching mudflow, pipe movement, pipevibration, predetermined amount of time or a combination thereof Thesecan be detected by any of various types of sensors, including, but notlimited to accelerometers, magnetometers, gyroscopes, current meters,sound detectors, vibration detectors and combinations thereof Uponsensing the onset of a triggering event, the sensor sends a signal to anactivation mechanism (to be described hereinafter) to activate thelifting buoyancy module. The sensor can be located in the system in anyconvenient location. For instance, the sensor can be attached to thesubsea pipeline or to at least one of the lifting buoyancy modules.Alternatively, the sensor can be located remotely and separately fromthe subsea pipeline. For instance, the sensor can be located on theseabed near the pipeline.

The activation mechanism for activating the lifting buoyancy modules canbe any of a number of mechanisms contemplated by the inventors. In someembodiments 10, as shown in FIGS. 1A and 1B and FIGS. 2A through 2E, thelifting buoyancy modules 12A are inflatable. In such embodiments, eachbuoyancy module 12A includes as the activation mechanism an inflator 16in communication with the sensor 18. The inflator 16 is capable ofinflating or increasing the internal volume of the buoyancy module 12A,thus activating the buoyancy module 12A as shown in FIG. 2B. Theinflator can utilize any of several suitable technologies. For instance,the lifting buoyancy modules can be collapsible and expandable buoyancyelement which can be inflated from a source of gas. The collapsible andexpandable buoyancy module 12A can be folded compactly to occupy aminimum volume when in its non-activated state as shown in FIG. 2A andFIG. 2C. Once activated, in response to a signal from the sensor 18, thebuoyancy module 12A is inflated resulting in a maximum volume. Theincrease in volume in turn increases the buoyancy force or lift forceapplied to the pipeline section. The buoyancy module 12A can bedeflated, refolded and repacked back to the non-activated state asrequired.

The inflation of the lifting buoyancy module 12A can be activated eithermanually (e.g., by divers, AUV or ROV), mechanically or chemically. Inone embodiment, an ignition causes a chemical reaction of two or morecomponents that can quickly generate gases. These gases inflate the bagand as a result generate buoyancy loads that lift the pipeline. Suitablegas generators or inflators 16 for use in the lifting buoyancy modulehave been described in references with respect to airbag inflators,e.g., for use in vehicles. For example, U.S. Pat. No. 6,572,143describes a gas generator for an air bag including an outer shellvessel, an ignition unit disposed within the vessel, pressurized gasstored in the vessel, and a pressurized gas accommodation chamber foraccommodating the pressurized gas. The outer shell vessel has openingsin both ends thereof. One end is attached to a cylindrical diffusernozzle having a gas discharge outlet communicating with the air bag inthe outer peripheral wall thereof and a sleeve member inside. Theignition unit is disposed inside the sleeve member. The pressurized gascan be an inert gas, for example, argon, nitrogen, helium, or the like.The gas generator can have a gas discharge chamber within which islocated a gas discharge unit. The gas discharge unit can be made of apyrotechnic vessel for accommodating a pyrotechnic therein and anichrome wire disposed in the pyrotechnic vessel and heated byelectrification. The top of the pyrotechnic vessel can be positionedclose to the brittle weak portion of a gas sealing plate within the gasgenerator so that the explosion force is concentrated on the brittleweak portion. The gas discharge unit operates upon receiving a signal sothat it ruptures the brittle weak portion of the gas sealing plate todischarge the gas, thus activating the lifting buoyancy module 12A. Inthe gas generator 16, a sensor supplies a detection signal to a controlunit which arithmetically calculates the detection signal to generate anoutput signal representative of the arithmetic operation result, and theoutput signal is supplied to the ignition unit. In this operation, aheating body within the igniter vessel is heated, thereby burning theignition unit to generate a gas. The pressure of the generated gas movesthe ignition body to rupture the gas tight-sealing wall. In thissituation, the pressurized gas of the pressurized gas accommodationchamber is injected into the lifting buoyancy module 12A. The inflatoror gas generator 16 can adjust the amount of supply gas by controllingthe operation of the gas discharge unit. For example, when the subseapressure is high, the lifting buoyancy module is inflated with anexcessive internal pressure. In such a case, the gas discharge unit ofthe gas generator is operated in response to the operating signal fromthe control unit. When the nichrome wire is heated in accordance withthe operating signal, then the pyrotechnic within the pyrotechnic vesselis ignited to produce an explosion force that ruptures the brittle weakportion of the gas sealing plate. As a result, the pressurized gasaccommodation chamber communicates with the gas discharge chamber sothat the gas within the pressurized gas accommodation chamber enters thegas discharge chamber through the ruptured opening and then dischargesfrom the discharge port of the gas discharge chamber to the surroundingsubsea environment. As a result, the lifting buoyancy module 12A isinflated with an appropriate internal pressure. Other referencesdescribing suitable gas generators or inflators 16 for use in thelifting buoyancy module 12A include, for example, U.S. Pat. Nos.7,002,262, 5,466,420, and 6,447,007. The system can allow thereplenishment of consumables such as gas, chemicals, etc. used in theprocess, which can be done by divers, AUV or ROV to enable multiple usesof the system.

FIG. 2C illustrates a clamp on device for attaching to a pipeline havingan inflatable lifting buoyancy module 12A. A sensor 18 is incommunication with a detonator or igniter 16A, which detonates inresponse to a signal from the sensor. Upon detonation or ignition, solidpropellant material 16B is ignited quickly generating gas to inflate thebuoyancy module 12A. The propellant material can be, for example, sodiumazide.

In an alternative embodiment, a mechanical activation mechanism can usea system of ribs (not shown) which act as energized springs that whenactivated would be released, changing their physical configuration toresult in an expanded buoyancy module reinforced by the ribs. In oneembodiment, the inflation of the lifting buoyancy module 12A can beactivated by a pressure accumulator (not shown) in fluid communicationwith the lifting buoyancy module 12A. A signal can be sent from thesensor 18 to open a valve in the pressure accumulator to inflate thebuoyancy module 12A. A gas is stored under high pressure in theaccumulator near the collapsed lifting buoyancy module in itsnon-activated state. Once the signal is sent from the sensor to open andinflate the buoyancy module, the gas will begin filling the buoyancymodule at a pressure lower than the pressure in the accumulator.

Regardless of the mechanism for inflating the lifting buoyancy module,the system is designed to operate and perform under subsea and marineconditions, especially in terms of hydrostatic pressure andenvironmental loading caused by environmental factors including localcurrents. The system is designed with high strength materials to providethe required robustness to sustain the internal and external loads andto safely and reliably exert the lifting load to raise the pipeline tothe desired height.

In one embodiment, as shown in FIGS. 2D (non-activated state) and 2E(activated state), the inflatable lifting buoyancy modules 12A can beradially disposed about the pipeline so that they surround the pipelineand inflate in the radial direction. In another embodiment, as shown inFIGS. 1A and 1B and FIGS. 2A and 2B, the inflatable buoyancy modules 12Acan be in the form of balloons attachable to the pipeline eitherdirectly, by tethers or by any other suitable attachment means as willbe apparent to one skilled in the art. The inflatable buoyancy modulescan be normally (i.e., in their non-activated state) folded into compactcapsules. The capsule can be installed on the pipeline with a clamp byan ROV during the pipelay operation or during a retrofitting operation.

In the case of inflatable buoyancy modules 12A, once activated and usedto avoid damage from a geo-hazard, the inflatable buoyancy modules canbe removed from the pipeline, e.g., by ROV, in order to return thepipeline to the seabed if desired.

In some embodiments 10′, for example that illustrated in FIGS. 3A and3B, the lifting buoyancy modules 12B do not require inflating to becomebuoyant, and in their normal, non-activated state are attached to thepipeline by a plurality of lifting tethers 4. The lifting buoyancymodules 12B are further attached reversibly to anchors 2 in the seabed 7by plurality of anchoring tethers 3. The anchors 2 can be anchor pilesor clamp weights in the seabed 7. While the anchoring tethers 3 areattached, in the non-activated state, the lifting buoyancy modules 12Bare constrained from lifting the subsea pipeline 1. In such embodiments,the activation mechanism is detaching at least a portion of theanchoring tethers 3 such that the buoyancy force is transferred to thedistributed lifting tethers 4 along the pipeline section of interest. Inone embodiment, the activation mechanism can be a link 20 within theanchoring tether 3 that can be disconnected in response to a signal fromthe sensor 18. The activated lifting buoyancy modules 12B havesufficient buoyancy force acting on the pipeline to lift the subseapipeline off the seabed to the design, predetermined height and lengthby way of the lifting tethers. In such embodiments, once activated andused to avoid damage from a geo-hazard, the lifting buoyancy modules canbe reattached to the anchors, e.g., by ROV, in order to return thepipeline to the seabed if desired.

In some embodiments 10″, for example, that illustrated in FIGS. 4Athrough 4D, the lifting buoyancy modules 12C do not require inflating tobecome buoyant, and in their normal, non-activated state are attached tothe subsea pipeline 1 and reversibly attached to non-buoyant weights 22such that when the lifting buoyancy modules 12C and the non-buoyantweights 22 are attached, the combination of the lifting buoyancy module12C and the non-buoyant weight 22 provides no more than neutral buoyancyforce applied to the pipeline. In one embodiment, the lifting buoyancymodules 12C attach to the non-buoyant weights 22 around the subseapipeline 1 in pairs of half-shell clamps. The lifting buoyancy modules12C and the non-buoyant weights 22 can also be reversibly attached bymeans of straps, bolts or the like. Alternatively, the non-buoyantweights 22 can be reversibly attached to the pipeline 1 and the liftingbuoyancy modules 12C can be fixedly attached to the pipeline. Thenon-buoyant weights 22 can be made of steel covered with a layer ofpolymeric material. The lifting buoyancy modules 12C and the non-buoyantweights 22 are detached from one another in order to activate thelifting buoyancy modules 12C. When the lifting buoyancy modules 12C andnon-buoyant weights 22 are detached from one another, the liftingbuoyancy modules 12C remain attached to the subsea pipeline 1. In suchembodiments, the activation mechanism is detaching at least a portion ofthe lifting buoyancy modules from the associated non-buoyant weightssuch that the subsea pipeline is lifted off the seabed. In oneembodiment, the activation mechanism 23 is any convenient means fordetaching the lifting buoyancy modules 12C from the non-buoyant weights22 in response to a signal from the sensor 18. In one embodiment, notshown, the non-buoyant weights 22 are each articulated, i.e., formed ofdiscrete segments joined together. Once detached, the articulatednon-buoyant weights 22 will lie flat on the seabed 7. Once activated andused to avoid damage from a geo-hazard, the non-buoyant weights 22 canbe reattached to the pipeline, e.g., by divers, AUV or ROV, in order toreturn the pipeline to the seabed 7 if desired.

The systems described herein also provide a way to manage dynamicfatigue-sensitive regions of structures such as sections near thetouchdown point of risers and pipeline over steep scarp crossings toalleviate damage or fatigue effects in anticipation of any change inoriginal design basis, excessive environmental or operating loading, orgeo-hazard that can lead to the accumulation or exacerbation of fatigueor that can lead to over-stress. In the system 400 illustrated in FIGS.5A and 5B, this can be accomplished through selective activation of thelifting buoyancy modules 12A to relocate the touchdown point of a riser122 and thereby redistribute stress and fatigue loads. A larger radiuscan be provided in the riser 122 by relocating the touchdown point. Inone embodiment, the stresses within the riser are managed over time byperiodically changing the number of buoyancy modules 12A attached to theriser and/or moving the regions along the riser in which liftingbuoyancy modules are activated. Although FIGS. 5A and 5B illustrate asystem utilizing inflatable lifting buoyancy modules 12A, any of theother lifting buoyancy modules described herein could also be utilized.

The lifting buoyancy modules can also be activated in the followingcases: significant change in original design basis, operating conditions(planned or unplanned) such as excessive shut down and start up, changesin flow regime that can induce higher cyclical stress due to, forexample, slugging, thermally induced loads or vibration, higher levelsof corrosive fluids such as H₂S than originally planned, and higheramount of motion in the system than originally planned. The liftingbuoyancy modules can be selectively activated to change the pipelineconfiguration either temporarily or permanently.

In one embodiment, again referring to FIGS. 1A and 1B, the systemfurther includes at least one buoy 13 having a global positioning system(GPS) transmitting device therein capable of being releasably attachedto the subsea pipeline, as shown in FIG. 1A. Upon activation of any orall of the lifting buoyancy modules, regardless of the embodiment of thelifting buoyancy modules used, the buoy can be released from the subseapipeline, as shown in FIG. 1B, and the GPS transmitting device cancommunicate with a satellite 21 and/or a receiving or monitoring device17 at a remote location. This functionality is especially advantageousto alert operators of the occurrence of a triggering event. Thisfunctionality is also advantageous for tracking and recording plannedactivations of lifting buoyancy modules in a record-keeping database. Inone embodiment, upon activation of at least a portion of the liftingbuoyancy modules 12A, the GPS buoy will be released, float to thesurface and transmit a signal 15 to inform personnel that the buoyancymodules 12A have been activated, and the location of the buoyancymodules activated. Furthermore, once the GPS buoy 13 is activated, textmessages and emails can be sent to inform the operations team viacellular antenna. This buoy system allows for communication to a vesselor an onshore location via radio antennae. The GPS buoy 13 can bepowered via battery (not shown) which will have rechargeablecapabilities via an AUV. Alternatively, the upward movement of the buoymay be leveraged to recharge the battery. Although FIGS. 1A and 1Billustrate a system utilizing inflatable lifting buoyancy modules 12A,any of the other lifting buoyancy modules described herein could also beutilized.

In an alternative embodiment, the system can include at least one subseaacoustic transmitting device (not shown). Upon activation of any or allof the lifting buoyancy modules, the subsea acoustic transmitting devicecan communicate an acoustic signal to a receiving or monitoring deviceat a remote location. In one embodiment, warning data can be transmittedto a control station.

The flowchart 600 of FIG. 6 illustrates methods according to someembodiments. In a first step 602, lifting buoyancy modules according toembodiments disclosed herein are attached to a pipeline or riser.Decision point 604 in the design of the system asks whether the systemis responsively activated (reactive) or not (planned or proactive). Ifyes, then the lifting buoyancy modules are sensor activated (610) andthe lifting buoyancy modules are set to a listening state (612) todetect a sense disturbance or a leading event (614) detected by thesensor. Such disturbances or leading events have been described herein.Upon detection of the disturbance or leading event, the lifting buoyancymodules will be activated (616). Upon activation in step 616, theactivated state of the lifting buoyancy modules will be communicated toa monitoring location or a database (618).

Still referring to the flowchart 600 of FIG. 6, when the system is notdesigned to be responsively activated, but rather proactively activated,then the lifting buoyancy modules are control system activated (605) andthe lifting buoyancy modules are set to a primed state in which they canreceive signals from the control system (606). Upon a signal being sentfrom the control system (608), the lifting buoyancy modules areactivated (616), and the activated state of the lifting buoyancy moduleswill be communicated to a monitoring location or a database (618).

An existing subsea pipeline can be retrofitted with any of the systemsdisclosed herein. The method for retrofitting includes attaching aplurality of lifting buoyancy modules to a subsea pipeline, wherein thebuoyancy module are activated according to any of the variousembodiments of systems described herein. The lifting buoyancy modulesand associated sensors can be installed with the assistance of an ROV,AUV or manually by divers.

EXAMPLE

A software package for the design and analysis of offshore marinesystems, OrcaFlex (commercially available from Orcina Ltd., Cumbria,UK), was used to simulate the effects of the lifting buoyancy modules ona pipeline. The pipeline grade was assumed to be DNV-OS-F101 (DNV codeassigned by Det Norske Veritas, Oslo, Norway).

The following table lists the inputs and the outputs when the simulationwas run.

TABLE Inputs Stress (MPa) 450 Allowable stress (MPa) 360 Elastic modulus(MPa) 212,000 Pipe outer diameter (mm) 762 Wall thickness (mm) 36.6Content density (kg/m³) 250 Depth (m) 740 Results Uplift force per buoy(te) 3.1 Number of buoys 30 Average lift height (m) 1.38 Maximum liftheight (m) 2.13 Length of pipeline at a height greater than 1.3 m (m)200 Maximum stress (kPa) 78,000 % Maximum allowable stress 22 % Maximumstrain 0.037

Unless otherwise specified, the recitation of a genus of elements,materials or other components, from which an individual component ormixture of components can be selected, is intended to include allpossible sub-generic combinations of the listed components and mixturesthereof. Also, “comprise,” “include” and its variants, are intended tobe non-limiting, such that recitation of items in a list is not to theexclusion of other like items that may also be useful in the materials,compositions, methods and systems of this invention.

From the above description, those skilled in the art will perceiveimprovements, changes and modifications, which are intended to becovered by the appended claims.

What is claimed is:
 1. A system for protecting subsea pipeline fromexcessive stress and/or fatigue loading, comprising: a plurality oflifting buoyancy modules capable of being attached to a subsea pipelinein a normally non-activated state and having an activation mechanismassociated there with; wherein the plurality of lifting buoyancy moduleshas sufficient buoyancy when at least a portion of the plurality oflifting buoyancy modules is activated to lift the subsea pipeline offthe seabed to a predetermined height over a predetermined length.
 2. Thesystem of claim 1, further comprising: at least one sensor incommunication with at least one of the activation mechanisms of theplurality of lifting buoyancy modules for detecting the onset of atriggering event and upon detecting the onset of a triggering event,sending a signal to the at least one activation mechanism to activatethe associated lifting buoyancy module to lift the pipeline.
 3. Thesystem of claim 2, wherein the sensor is selected from the groupconsisting of an accelerometer, a magnetometer, a gyroscope, a currentmeter, a sound detector, a vibration detector and combinations thereof.4. The system of claim 2, wherein the sensor is attached to the subseapipeline or at least one of the plurality of lifting buoyancy modules.5. The system of claim 2, wherein the sensor is located on the seabedremote from the subsea pipeline.
 6. The system of claim 1, furthercomprising: at least one signaling buoy having a global positioningsystem transmitting device therein capable of being releasably attachedto the subsea pipeline; wherein upon activation of any or all of thelifting buoyancy modules, the signaling buoy is detached from the subseapipeline and rises to the sea surface whereupon the global positioningsystem transmitting device in the signaling buoy communicates with areceiving device at a remote location.
 7. The system of claim 1, furthercomprising: at least one subsea acoustic transmitting device; whereinupon activation of any or all of the lifting buoyancy modules, thesubsea acoustic transmitting device communicates with a receiving deviceat a remote location.
 8. The system of claim 1, wherein each of theplurality of lifting buoyancy modules is further capable of beingreversibly attached to an anchor in the seabed by an anchoring tethersuch that the lifting buoyancy modules are constrained from lifting thesubsea pipeline; and wherein the activation mechanism associated withthe plurality of lifting buoyancy modules comprises detaching at least aportion of the anchoring tethers such that at least a portion of thelifting buoyancy modules are unconstrained and thereby lift the subseapipeline.
 9. The system of claim 8, wherein each of the plurality oflifting buoyancy modules is further capable of being attached to thesubsea pipeline by a lifting tether such that when the at least aportion of the anchoring tethers is detached the subsea pipeline islifted by the at least a portion of the lifting buoyancy modules by wayof the lifting tethers.
 10. A method for protecting subsea pipeline fromexcessive stress and/or fatigue loading, comprising: attaching aplurality of lifting buoyancy modules having an activation mechanismassociated there with to a subsea pipeline; wherein the plurality oflifting buoyancy modules has sufficient buoyancy when at least a portionof the plurality of lifting buoyancy modules is activated to lift thesubsea pipeline off the seabed to a predetermined height over apredetermined length.
 11. The method of claim 10, further comprising:providing at least one sensor in communication with at least one of theactivation mechanisms of the plurality of lifting buoyancy modules;using the at least one sensor to detect the onset of a triggering event;and upon detecting the onset of a triggering event, sending a signalfrom the at least one sensor to the activation mechanism of at least oneof the plurality of lifting buoyancy modules to activate the liftingbuoyancy module.
 12. The method of claim 11, wherein the sensor isselected from the group consisting of an accelerometer, a magnetometer,a gyroscope, a current meter, a sound detector, a vibration detector andcombinations thereof.
 13. The method of claim 11, wherein the sensor isattached to the subsea pipeline or at least one of the plurality oflifting buoyancy modules.
 14. The method of claim 11, wherein the sensoris located on the seabed remote from the subsea pipeline.
 15. The methodof claim 10, further comprising releasably attaching to the subseapipeline at least one signaling buoy having a global positioning systemtransmitting device therein, wherein upon activation of any or all ofthe lifting buoyancy modules, the signaling buoy is released from thesubsea pipeline and the global positioning system transmitting devicecommunicates with a receiving device at a remote location.
 16. Themethod of claim 10, further comprising reversibly attaching each of theplurality of lifting buoyancy modules to an anchor in the seabed by ananchoring tether such that the lifting buoyancy modules are constrainedfrom lifting the subsea pipeline; wherein the activation mechanismassociated with the plurality of lifting buoyancy modules comprisesdetaching at least a portion of the anchoring tethers from the liftingbuoyancy modules such that at least a portion of the lifting buoyancymodules are unconstrained and thereby lift the subsea pipeline.
 17. Themethod of claim 16, wherein each of the plurality of lifting buoyancymodules is further attached to the subsea pipeline by a lifting tethersuch that when the at least a portion of the anchoring tethers isdetached the subsea pipeline is lifted by a portion of the liftingbuoyancy modules by way of the lifting tethers.